In a certain class of imaging devices, known as off axis inkjet printers, liquid colorant is delivered from a reservoir to an imaging head through a fluid carrying member, such as a tube. The reservoir and the imaging head are separated to reduce the mass of the imaging head and allow lower cost replenishment of the ink in the inkjet printer. Through a variety of ways, voids can form in the liquid colorant. These voids can interfere with the proper working of the imaging head. Another possible problem is that replacement of an ink reservoir is done improperly so that liquid colorant cannot flow from the reservoir to the imaging head. A need exists for a method and apparatus to detect voids within a fluid carrying member.